CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 62/256,302, filed November 17, 2015. The contents of the referenced application are incorporated into the present application by reference.

FIELD

[0002] The presently disclosed subject matter relates to methods and catalysts for conversion of ethane to ethylene.

BACKGROUND

[0003] Ethylene can be used for production of bulk-chemicals, e.g., poly-ethylene and ethylene oxide. Conventional methods of converting ethane to ethylene include ethane steam cracking. However, steam cracking is highly endothermic and deposits coke fragments within the reactor. Another process of ethylene production is catalytic oxidative conversion of ethane as shown below:

C ₂ H ₆ + 0.5O ₂ C ₂ H ₄ + H ₂ 0

C ₂ H ₆ + 2.50 ₂ 2CO + 3H ₂ 0

C ₂ H ₆ + 3.50 ₂ 2C0 ₂ + 3H ₂ 0

[0004] However, one drawback of this approach is that known catalysts are not stable for a long time at the necessary reaction temperatures. The catalyst becomes deactivated and decreases ethylene selectivity. The reaction is also highly exothermic and leads to runaway of heat within a fixed bed reactor.

[0005] Ethane dehydrogenation can also be carried out using C0 ₂ as an oxidant instead of 0 ₂ . However, this process leads to side reactions as shown below:

2C ₂ H ₆ + 2C0 ₂ CO + 3H ₂ 0 + C [0006] This formation of coke fragments builds up on reactor coil walls and requires a shut down every 2 to 3 months to clean the coils. Further, the reaction is highly endothermic and not energy efficient.

[0007] Therefore, there remains a need in the art for methods and catalysts to convert ethane to ethylene more efficiently and reduce reactant consumption. The presently disclosed subject matter solves this problem with methods and catalysts for converting ethane.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0008] The presently disclosed subject matter provides for a process for ethane dehydrogenation which can include feeding a gas stream into a reactor comprising a catalyst, wherein the gas stream comprises C ₂ H ₆ , C0 ₂ , and 0 ₂ . The process can further include contacting the gas stream to the catalyst in the reactor, wherein the catalyst is a mixed metal oxide catalyst, and reacting C ₂ H ₆ with C0 ₂ and 0 ₂ present within the gas stream to produce ethylene, at a temperature of from about 400° C to about 900° C.

[0009] In certain embodiments, the catalyst is a K-Cr-Mn-0/Si0 ₂ catalyst. In certain embodiments, the catalyst contains from about 2% to about 4% K, from about 5% to about 8% Cr, and from about 14% to about 20%Mn-O. In other embodiments, the catalyst is 2% K-6% Cr-14% Mn-0/Si0 ₂ .

[0010] In certain embodiments, 0 ₂ is sourced from air.

[0011] In certain embodiments, the gas stream comprises 30% C ₂ H ₆ /30% CO ₂ /40% air.

[0012] In certain embodiments, the temperature is about 780° C or less. In other embodiments, the temperature is about 780° C.

[0013] In certain embodiments, the reactor operates at a space velocity from about 1 to about 5000 h ^"1 . In certain embodiments, the reactor operates at a space velocity of about 1800 h ^"1 .

[0014] In certain embodiments, the reaction is performed from about 30% to about 99% conversion of C0 ₂ or about 49% conversion of C0 ₂ .

[0015] In certain embodiments, the reaction is performed from about 50% to about 99% mol conversion of ethane or about 70% mol conversion of ethane.

[0016] In certain embodiments, ethylene selectivity is from about 35 to about 99%. In other embodiments, ethylene selectivity is about 65%.

[0017] In certain embodiments, the reactor is a fixed bed reactor or a quartz reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic representation of one exemplary process of the presently disclosed subject matter. DETAILED DESCRIPTION

[0019] There remains a need in the art for new methods and catalysts for converting ethane to ethylene. The presently disclosed subject matter provides methods and catalysts for the conversion of ethane to ethylene via conjugation of exothermic catalytic oxidative conversion and endothermic ethane dehydrogenation with C0 ₂ . The total reaction of the integrated processes can be represented by the following equation:

2C ₂ H ₆ + C0 ₂ + 0.5C-2 2C ₂ H ₄ + CO + 2H ₂ 0.

[0020] As used herein, the term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5%), and or up to 1% of a given value.

Catalysts

[0021] Catalysts suitable for use in conjunction with the presently disclosed matter can be catalysts capable of catalyzing oxidative conversion with 0 ₂ and endothermic ethane dehydrogenation with C0 ₂ . [0022] In certain embodiments, the catalyst can be a solid catalyst, e.g., a solid-supported catalyst. The catalyst can be a metal oxide or mixed metal oxide. In certain embodiments, the catalyst can be located in a fixed packed bed, i.e., a catalyst fixed bed. In certain embodiments, the catalyst can include solid pellets, granules, plates, tablets, or rings.

[0023] In certain embodiments, the catalyst can include one or more transition metals. In certain embodiments, the catalyst can include a mixture of oxides of redox elements, modified by one or more alkali metals. The catalyst can include manganese (Mn) and chromium (Cr) oxides. In certain embodiments, the catalyst can be modified by potassium (K). In certain embodiments, the catalyst can contain from about 10 to about 30 % Mn. In certain embodiments, the catalyst can contain from about 14 to about 20 % Mn. In certain embodiments, the catalyst can contain from about 1 to about 10 % K. In certain embodiments, the catalyst can contain from about 2 to about 4 % K. In certain embodiments, the catalyst can contain from about 1 to about 15 % Cr. In certain embodiments, the catalyst can contain from about 5 to about 8 % Cr. In certain embodiments, the catalyst includes 2% K, 6% Cr, 14% Mn-O.

[0024] In certain embodiments, the catalyst can include a solid support. That is, the catalyst can be solid-supported. By way of non-limiting example, the solid support can constitute about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% of the total weight of the catalyst. In certain embodiments, the solid support can be MgO, La ₂ 0 ₃ , Si0 ₂ , and/or A1 ₂ 0 ₃ . In certain embodiments the catalyst is 2% K, 6% Cr, 14% Mn-0/Si0 ₂ .

[0025] The catalysts of the presently disclosed subject matter can be prepared according to various techniques known in the art. For example, metal oxide catalysts suitable for use in catalyzing exothermic catalytic oxidative conversion and endothermic ethane dehydrogenation with C0 ₂ can be prepared from various metal nitrates, metal halides, metal salts of organic acids, metal hydroxides, metal carbonates, metal oxyhalides, metal sulfates, and the like. In certain embodiments, a transition metal (e.g., Mn) can be precipitated along with a solid support (e.g., Si0 ₂ ). In certain embodiments, catalysts can be prepared by precipitation of metal nitrates.

Reaction Mixtures

[0026] The presently disclosed subject matter provides methods of preparing ethylene from ethane.

[0027] As used herein, a "reaction mixture" can include ethane, C0 ₂ , and 0 ₂ . The C0 ₂ in the reaction mixture can be derived from various sources. In certain embodiments, the C0 ₂ can be a waste product from an industrial process. Ethane can be derived by using any extraction procedures known in the art, for example, pressure swing adsorption (PSA). 0 ₂ can be a stream of pure 0 ₂ and/or a stream of air, which includes 0 ₂ .

[0028] Reaction mixtures suitable for use with the presently disclosed methods can include various proportions of ethane, C0 ₂ , and 0 ₂ . In certain embodiments the reaction mixture can include from about 1 to about 50%, from about 10 to about 40%, or about from about 20 to about 30%) C ₂ H ₆ . In certain embodiments the reaction mixture can include from about 1 to about 50%), from about 10 to about 40%, or about from about 20 to about 30%> C0 ₂ . In certain embodiments the reaction mixture can include from about 1 to about 50%, from about 10 to about 40%), or about from about 20 to about 30%> 0 ₂ or air. In certain embodiments the reaction mixture can include about 30%> C ₂ H ₆ , about 30%> C0 ₂ , and about 40% air. Methods of forming ethylene from ethane

[0029] The methods of the presently disclosed subject matter include methods of preparing ethylene. In one embodiment, an exemplary method can include providing a reaction chamber. The reaction chamber can include a catalyst, as described above. The method can further include feeding a reaction mixture, as described above, to the reaction chamber. The method can additionally include contacting the reaction mixture with the catalyst at a reaction temperature from about 600 °C to about 900 °C, or from about 750 °C to about 800 °C. In certain embodiments, the reaction temperature is about 780 °C.

[0030] C0 ₂ , H ₂ , and ethane can be fed into the reaction chambers at various flow rates and space velocities. The space velocity can be varied, as is known in the art. In certain embodiments, the space velocity can be from about 1 to about 5000 h ^"1 . In certain embodiments, the space velocity can be from about 500 to about 2500 h ^"1 . In certain embodiments, the space velocity can be about 1800 h ^"1 .

[0031] The reaction can proceed with partial conversion of C0 ₂ and ethane, thus providing a product mixture that includes ethane, ethylene, CO, and C0 ₂ . In certain embodiments, the reaction can be performed from about 30% to about 99% conversion of C0 ₂ . In certain embodiments, the reaction can be performed to about 49% conversion of C0 ₂ . In certain embodiments, the reaction can be performed from about 50% to about 99% mol conversion of ethane. In certain embodiments, the reaction can be performed to about 70% mol conversion of ethane.

[0032] In certain embodiments, the reaction can be selective for production of ethylene. In certain embodiments, the ethylene selectivity is from about 35 to about 99%. In certain embodiments, the ethylene selectivity is about 65%.

[0033] For the purpose of illustration and not limitation, FIG. 1 is a schematic representation of a method according to one non-limiting embodiment of the disclosed subject matter. In certain embodiments and as shown in FIG. 1, the method 100 can include feeding a gas stream, e.g., C ₂ H ₆ , C0 ₂ , and 0 ₂ , into a reactor comprising at least one catalyst 101. In a further embodiment, the method includes contacting the gas stream to at least one catalyst in the reactor 102, and the at least one catalyst is a mixed metal oxide catalyst, e.g., a K-Cr-Mn-0/Si0 ₂ catalyst. The method can also include reacting the C ₂ H ₆ with C0 ₂ and 0 ₂ present within the gas stream to produce ethylene 103, and reaction temperature can be from about 400° C to about 900° C, e.g., 780° C.

[0034] The methods and catalysts of the presently disclosed subject matter can have advantages over other techniques for ethylene production. The presently disclosed subject matter includes the surprising discovery that catalysts containing K-Cr-Mn-0/Si0 ₂ can catalyze the reaction of ethane with both 0 ₂ and C0 ₂ to produce ethylene. The combination of an exothermic and an endothermic reaction reduces the formation of C0 ₂ from ethane and consequently reduces the formation of coke fragments which cause catalyst deactivation. The overall reaction is only slightly exothermic, e.g., -10 kcal/mol, and reduces oxygen consumption, feed costs, and overall process economics.

[0035] As demonstrated in the Examples, the methods of the presently disclosed subject matter can provide ethylene from ethane with good selectivity and high conversion.

EXAMPLES

EXAMPLE 1 - Conversion of ethane

[0036] In this Example, ethane is converted to ethylene with a catalyst.

[0037] Ethane was reacted with a gas mixture in the presence of a catalyst. The gas mixture comprised 30% C ₂ H ₆ /30% CO ₂ /40% air. The catalyst was 2% K-6% Cr-14% Mn- 0/Si0 ₂ loaded at 7 ml in a fixed bed quartz reactor. The reaction proceeded at 780° C with a space velocity of 1800h ^_1 . Gas flow was from the top of the reactor and after the reactor, a small stream of gas flow at 25 cc/min was connected to a gas chromatograph (GC) for analysis. All the components of the gas including C ₂ H ₆ , C ₂ H ₄ , C0 ₂ , CO and H ₂ were analyzed via GC. Water was not analyzed.

[0038] Conversion and selectivity were calculated on the basis of mole percentage of concentration of each of the components in the product. The following formulas were used to calculate conversion and selectivity: C ₂ H ₆ conversion, %mol= (% mol C ₂ H ₆ in the inlet-%mol C ₂ H ₆ in the outlet)/%mol C ₂ H ₆ in the inlet

C ₂ H ₄ selectivity, mol%= %mol C ₂ H ₄ / (%mole C ₂ H ₆ in- %mole C ₂ H ₆ out) C0 ₂ conversion, mol%= (%mol C0 ₂ in-%mol C0 ₂ out)/%mol C0 ₂ in

[0039] Ethane conversion was 70% mol while C0 ₂ conversion was 49% mol. Selectivity for ethylene was 65% and the overall ratio of CO to ethylene in the final product was 1.2.

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[0040] Although the presently disclosed subject matter and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosed subject matter as defined by the appended claims. Moreover, the scope of the disclosed subject matter is not intended to be limited to the particular embodiments described in the specification. Accordingly, the appended claims are intended to include within their scope such alternatives.